Road structure and process of making



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J. S. BURDGE.

ROAD STRUCTURE AND PROCESS OF MAKING. APPLICATION FILED APR-5, 1920.

Patented Sept. 6, 1921 such materials as are available.

PATENT OFFICE.

JEFFERSON S. BURDGE, F HUNTINGTON PARK, CALIFORNIA.

ROAD STRUCTURE AND PROCESS OF MAKHTG.

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Application filed April 5, 1920. Serial no. 371,406.

To all whom it may concern:

Be it known that I, JEFFERSON S. BURDGE, citizen of the United States, residing at Huntington Park, in the county of. Los Angeles and State of California, have invented certain new and useful Improvements in Road Structure and Processes of Making, of which the following is a specification.

The present invention relates to the production of permanent and wear-resisting road pavements, and has for its object the production of roads of improved permanence, stability, and wear-resistance.

In preparing roads according to the pres-1 ent invention, a suitable foundation is first prepared in any approved manner and of This foundation may be prepared in any known manner, and may be rolled or otherwise compacted, if desired.

Upon the foundation is placed a layer'constituting the lower portion of the finished wearing surface, this lower portion being preferably composed of the following materials in approximately "the following proportions:

Coarse aggregate, which may be either crushed rock or slag, crushed or uncrushed gravel, passing a two inch screen, but retained by a one-fourth inch screen, 45 to 60%.

Medium aggregate, which may be either crushed rock or slag, crushed or uncrushed sand passing a one-fourth inch gravel, or screen and retained by a one-tenth inch screen, to

Fine aggregate, which may be either crushed gravel, sla or rock, or sand passin" a one-tenth inc screen, to 38%.

itumin'ous cement, 5 to 7%.

The bituminous cement employed in this lower portion should be of such a character that it will become thoroughly molten at a temperature of 350 F., or less, and the amount stated above is found to be entirely sufficient for producing the structural, weight sustaining, portion. Upon this is placed the wear-resisting or finishing portion.

Preferably the materials forming the lower portion are previously thoroughly mixed and applied to the roadway while hot, so that the bituminous cement will be soft and plastic. The thickness of the layer forming the first portion will depend upon the character of the foundation upon which Specification of Letters Patent.

displacement resisting Patented Sept. 6, 19211.

it is laid and the amount and the character of the trafiic to which it is to be subjected, but generally a depth of from 1 to 3 inches is to be preferred. It should contain about or say 45 to of coarse aggre ate, and it is advisable that the largest of pieces of the mineral aggregate in the structural portion should be of a size equal to about one half of the depth or thickness of the completed wearing surface. The aggregate, stone, gravel, or slag, sand, etc., employed in the lower portion are preferably, heated to about 200 to 400 F., and mixed roughly whereupon the bituminous cement is added preferably in a molten condition, and the mass then mechanically mixed while at a temperature at which the bituminous cement is liquid or semi-liquid until a uniform mixture is produced, and this mixture is then spread preferably while hot upon the foundation to give the desired depth, and with its surface true to grade and contour. lit is usually advisable not to compress or roll the lower portion at this sta e. h I V The nishing or wear-resisting portion is then spread on the structural portion and this finishing portion consists of .natural bituminous or asphaltic sand or rock, reduced to a granular condition by either pulverization or heat, that is to say, mineral matter, which is naturally impregnated or coated with bituminous material, which natural bituminous rock or sand is known to possess remarkable properties of resistance to abrasion, 'such as is produced by traffic, but which by itself, is open to the objection of lacking-stability and resistance to displacement or rutting under trafiic.

In the production of the finishing portion I preferably add on top of the uncompacted lower portion a thin mat of this material, this being preferably applied while the lower portion is still hot,-that is to say, before the bituminous cement therein has hardened or set. There are various kinds of natural bituminous or asphaltic sand or rock, which may be employed for this upper coarse, but it is preferable to use a material, the particles of which are thoroughly impregnated with pure asphaltum in such amount that 10 to 20% by weight of the material is soluble in carbon disulfid. If the natural bituminous or asphaltic sand or rock contains a substantially greater or less percentage of the soluble material than above specified, then the . section of a road constructed in accordance it is advisable, for example during the grinding, pulverizing or heating operation, to add either a'suificient quantity of fine sand or crushed stone screenings or to addbituminous cement or a thick asphaltic oil in liquid form to secure a product within the range above stated. Obviously, the sand, crushed stone bituminous cement or oil could be added at any other convenient stage of the operation, before spreading. The thickness of the wear-resisting portion will depend upon the amount and character of the travel which the road is to stand, prevailing temperature conditions and the like,

but for ordinary purposes should be spread to a depth of from one fourth to threefourths of an inch. The material forming this upper portion may be heated prior to spreading the same, but it is preferable to spread the same at ordinary atmospheric temperature, the spreading being performed I while the material of the lower portion is still hot, as above stated.

The entire structure is then compressed as a unit, preferably by means of a self-propelled heavy roller until the finished wearresisting portion and the lower structural portion become thoroughly compacted and completely united with each other. The operation of compression causes the natural bituminous or asphaltic sand or rock to become semi-plastic or plastic, due in/part to heat developed by friction betweenthe component particles of the structure during the process of compression and in part to the transmission of heat from the previously heated material forming the structural portion. WVhile in this plastic-condition, the grains of the upper portion are found to thoroughly unit with each other and to be thoroughly bonded to the lower structural portion. I 1

After the finishing portion has been thoroughly compressed while it is still in a slightly plastic condition a light sprinkling of crushed stone, Portland cement, sand, gravel or pulverized stone or slag may, if desired, be uniformly applied and rolled into the same.

During the rolling or compacting operation the fine material constituting the top portion will enter the voids or cavities in the upper part of the lower portion to some extent thereby producing a very effective bonding of the upper and lower portions. It is to be understood, however,'that considerable of the upper portion remains above the coarse material of the lower or structural portion. The amountdepending upon the condition of the lower portion and the depth.

of the material used for the upper portion. The annexed drawing illustrates a cross with a preferred embodiment of the present invention. In said drawing, 1 represents the foundation, 2 represents a suitable lower or structural portion,.this being composed of coarse aggregate, 3; medium aggregate, 4; and fine aggregate 5; proportioned preferably as above described and mixed with from 5 to 7% of bituminous cement,-and 6 represents the surfacing or wear-resisting portion. I call attention to the zone between the lines 7 and 8, in which the two layers become thoroughly blended and united and bonded together, by compression. In the surface may be located the hard fine material 9, if desired.

I am, of course, familiar with bituminous or asphaltic concrete pavements, but I believe that the use of natural bituminous or asphaltic sand or rock, applied as above specified, as an abrasion-resisting surfacing,

- is an entirely new addition to the road building art.

While the lower structural portion described above, has been shown by tests. which have been made, to be especially suitable for use in my invention, I do not restrict myself to this particular lower structural portion because any other bituminous mixture or bituminous coated road body which has sufficient weight-sustaining and displacement-resisting strength may also be used as the lower structural portion, therefore the application of such finely divided (granular or pulverized) natural asphaltic orbituminous rock or sand to any suitable bituminous mixture or bituminous coated road body, by the method herein described is within the scope of my invention.

' As stated above, it is advisable to .apply the wear-resisting upper portion upon the lower structural portion, while the latter is still in a heated condition (say, at between 200 and 400 F.). However, I do not restrict myself to this temperature range in the lower structural portion at the time of application of the material to constitute the wear-resisting portion and at the time of the compression of the pavement, since the primary object is to facilitate the proper blending and bonding together of the upper and lower portions of the pavement, during compression.

This bonding can be. obtained when-the bituminous cement in the lower structural portion is sufiiciently hot and plastic to blend .with the bituminous or asphaltic cement of the fine material constituting the upper portion. Accordingly any temperature at which the bituminous cement in the lower struca considerable extent upon the character of" the bituminous cement present in the lower or structural portion.

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'layer of cold, natural bituminous or as- I claim:

1. The improvement in. road-buildin which comprises the step of applying natural bituminous or asphaltic sander rock in a granular condition in such amount as v to leave a thin wear r'esisting surfacing por. tion composed essentially of such material to a manufactured bituminous or asphaltic concrete pavement structure, while the latter is still hot.

2. The improvement in road-building which comprises the steps of applying ahalticfsand or rock in a granular condition, in such amount as to leave -a thin wear-re sistin g' surfacing portion composed essentially of such material to a lower structural portion of a manufactured bituminous pr asphaltic concrete pavement structure, whlle the latter is hot, and then compressing the structure, whereby said upper portion; becomes heated and plastic during the process of laying over and compression into the heated, lower structural portion.

3. In'the manufacture of a road, the process which comprises first spreading a structural portion comprising coarse fine mineral aggregate and bituminousxcement, such spreading being effected while the material is suflicientlyhot for the cement to be plastic, then spreading thereupon, without previous compacting, a: relatively thin pore tion' of natural bituminous rock-or sand, 1n a granular conditiorn'and then compacting the compound structure while the lower layer is still hot. i

4. In the manufacture of a road, the 1mprovement which comprises spreadlngon a hot lower portion, a cold natural bituminous rock or sand, in a granular condition, and then compacting while the heat of the lower portion is retained in the mass.

5. Pi process of building a road structure which comprises spreading and grading a hot road-building material as a loose noncompacted body, then spreading thereupon a cold finely divided natural bituminous rock or sand, such second mentioned product being applied while the first mentioned material is in a hot. non'comp'acted condition, and then compressing the entire structure to effect a blending and densiiication. of the constituent parts or" the said road structure, while the cold top material becomes heated and rendered plastic by the heat contained in the hot lower material.

6. A process or building a road structure which comprises spreading and grading a ma m which comprises a spreading bituminousroad-building material, then spreading thereupon a finely divided natural bituminous rock or sand in such amounts as to leave a surfacing portion consisting essentially thereof and then compressing the en tire structure to efiect a blending and densification of the constituent parts of said road structure.

8. in the constructionof roads, the herein described improvement which comprises spreading comminuted natural bituminous rock or sand upon a lower structural portion, and then compressing the same, both of said operations being performed while said lower structural portion is at a temperature at which the bitumen content vo'lf such comminuted material can flow.

9. A composite road structure, comprising' a lower structural portion and an upper wear-resisting portion, such lower portion comprlsmg I Coarse mineral aggregate 4:5 to 60% Medium mineral aggregate to 2} inch size 10 to 15% Fine mineral aggregate less than inch size 20 to 38% Bituminous 'cement 5 to 7 and such upper portion consisting essentially oi compacted natural bituminous rock or sand, containing 10 to 20% of loitumen soluble in carbon disultid.

10. A complete pavement wearing surface having a lower structural portion consisting essentially of manufactured bituminous or asphaltic concrete or macadam or mortar,

and an upper wear-resisting surfacing por- JEFFERSON S, BURDGE. [In

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